The invention relates to a dual independent phasing system for independently adjusting the phase angle of both the intake and exhaust camshafts of a inner and outer camshafts of a concentric camshaft.
It is known to use two axially spaced apart camshaft phasers in connection with inner and outer shafts of a concentric camshaft assembly in order to separately adjust the timing of the inner and outer camshafts. This allows the timing of the intake and exhaust valves to be adjusted to obtain improved torque/power as well as improved emissions. Further, this arrangement provides additional benefits in engine idle stability and fuel economy.
Camshaft phasers that operate according to the vane-cell principle for single camshafts are known. These are described in publications by the assignee of the present invention, including U.S. Pat. No. 6,805,080, which is incorporated herein by reference as if fully set forth.
One known system for adjusting the control timing of a concentric camshaft assembly is described in DE 10 2005 039 751 A1. In this publication, a camshaft phaser located at the front of the engine is connected to an outer shaft of a co-axial camshaft arrangement and a second camshaft phaser located at the rear of the engine includes an outer housing that is connected to the outer camshaft and an inner rotor that is connected to the inner camshaft. This arrangement provides separate phasers which allows for easier control; however, it involves more difficulty in accessing the rear camshaft phaser as well as more complicated assembly and engine compartment space requirements.
DE 10 2006 024 793 A1 generically describes a dual phasing system for a concentric camshaft assembly which includes two camshaft phasers which are located at the front of an engine and are axially spaced adjacent to one another. The two camshaft phasers allow independent control of the outer and inner co-axial camshafts relative to the crankshaft in order to separately adjust the timing of the intake and exhaust valves of the internal combustion engine. The arrangement provides a specific spool valve control located within the inner camshaft for controlling the flow of hydraulic fluid to both the first and second camshaft phasers.
DE 10 2006 028 611, also discloses two camshaft phasers located axially adjacent to one another at the front of a concentric camshaft assembly of an internal combustion engine. The first camshaft phaser is connected to a front camshaft bearing arrangement which includes oil passages for delivering hydraulic fluid to and from the camshaft phaser for the outer camshaft. Hydraulic fluid for controlling the camshaft phaser connected to the inner camshaft is delivered via internal hydraulic fluid passageways located between the outer and inner camshafts and inside the inner camshaft which are supplied with hydraulic fluid through a separate camshaft mounting bearing arrangement.
These previously known dual independent phasing systems for concentric camshafts suffer from a number of drawbacks with respect to space requirements and ease of assembly to the front of a camshaft as a single assembly. Further, the prior known arrangements suffer from high external oil leakage due to the attachment method of the vanes to the covers of the camshaft phasers. Further, no system is provided for independently controlling the camshaft phasers for the inner and outer shafts so that they can be locked in base positions. Further, it would be beneficial to provide a dual independent phasing system which fits in roughly the same space within the engine assembly as a standard phaser so that additional space allocation with the engine compartment is not required.